1. Field of The Invention
The present invention relates generally to an instrument for quantitative analysis, which monitors light emission occuring due to a chemical reaction between a sample and a reagent(s) for performing quantitative analysis of the sample.
2. Description of The Prior Art
As is well known, various luminescent phenomena, which occur in chemical reactions of chemiluminescent materials, such as a luminol, a lucigenin, an uranine and so forth, with oxidizing agents, have been used for analyses of various unknown materials. In particular, the luminol has been used for analyses of bloodstains since hemoglobin in blood serves as a catalyst in the luminescent reaction of the luminol. The luminol reacts with hydrogen peroxide with the aid of a catalyst, such as potassium ferricyanide and so forth, to cause chemiluminescence. By using this chemiluminescence of the luminol, the hydrogen peroxide content can be determined. Moreover, the luminol reaction can be used for analyses of various metals, such as a cobalt (Co.sup.2+), a copper (Cu.sup.2+), a nickel (Ni.sup.2+), a chromium (Cr.sup.3+), an iron (Fe.sup.2+) and so forth. Enzymes, such as a peroxidase and so forth, can effectively function as a catalyst in the reaction of the luminol with the hydrogen peroxide. Therefore, if various materials, such as a protein, a hormone and so forth, are labelled with the enzyme in a similar manner to the EIA (Enzyme Immunoassay) Method, the content of unknown materials can be determined. In addition, it is well known that luciferin, which is a bioluminescent material, reacts with luciferase in the presence of adenosine triphosphate to cause a luminescent phenomenon. By using this phenomenon, the adenosine triphosphate content can be determined.
In the aforementioned luminescent phenomena, various luminescent patterns are observed in accordance with concentration or PH of buffer solution including the luminescent material and the catalyst, or the sort of luminescent material, or the mixing ratio of the reagent to the buffer solution. The relationship between time and quantity of emitted light (CPS) in a typical biochemical luminescent phenomenon is shown in FIG. 7. As shown in FIG. 7, as time goes by, the quantity of emitted light (CPS) increases suddenly from a mixing time t.sub.0 in which a sample to be determined is mixed with a reagent, reaches the maximum value (CPS).sub.MAX at a time t.sub.1, and thereafter decreases gradually. In order to accurately measure the quantity of emitted light shown in FIG. 7, it is necessary to detect the initial quantity of the emitted light (CPS.sub.MAX) at the time t.sub.1 immediately after the sample is mixed with the reagent.
The quantities of the emitted light in the aforementioned luminescent phenomena are generally measured by using the sensor of a photomultiplier tube and so forth, after the sample and the reagent are pipetted into cells or test tubes by means of a manually operable pipette available on the market.
However, according to the aforementioned process in which the pipetting of the sample and reagent is performed by means of the manually operable pipette, it is difficult to measure the initial quantity of the emitted light since the introduction of the materials into the cell requires a lot of time. In particular, in bioluminescent phenomena, the time in which the quantity of emitted light reaches the maximum value is very short. Therefore, in such phenomena, the initial quantity of emitted light can not accurately be measured.
In cases where a very dilute, for example, less than nanomole per liter (10.sup.-9 M) sample is determined by using chemiluminescent materials, the intensity of emitted light is very weak. Therefore, a very small quantity of photons, for example, less than ten photons per second, must be counted. In order to count such a small quantity of photons, it is required to decrease the quantity of unwanted light incident upon the optical sensor of the photomultiplier tube or the like from the outside of the measurement chamber, in which a cell, a cell holder and the optical sensor and so forth are housed, as much as possible. Therefore, the measurement chamber must be enclosed within a tightly covered black box so that no light can be introduced into the chamber from the outside.
In order to accurately count the initial quantity of the light emitted immediately after the sample is mixed with the reagent, and in order to decrease the quantity of the light from the outside of the chamber incident upon the optical sensor, the measurement chamber must comprise a black box, and an automatic pipetting device for injecting the sample and/or the reagent into the cells. The black box is provided with a port for introducing the cell at a location in which the cell introduced into the black box through the port does not obstruct the needles of the automatic pipetting device or Teflon tubes connected to the needles. The cell is horizontally moved from the cell introducing port to an injecting position in which the sample and/or the reagent are to be pipetted into the cell, and thereafter they are injected into the cell and the quantity of emitted light begins to be measured. If such an automatic pipetting device is used, the initial quantity of emitted light (the maximum value) can be measured, even when the quantity of emitted light suddenly changes immediately after the sample is mixed with the reagent. Moreover, by using such a black box, the quantity of light incident upon the optical sensor from the outside of the chamber can be decreased. However, according to this method, it is difficult to prevent light from being introduced into the black box from the outside when the cell is taken in and out the black box. When light introduced into the black box strikes a delicate photoelectric surface of the optical sensor of the photomultiplier tube which is designed to monitor weak light, the photomultiplier tube can become damaged or broken.
Moreover, in the aforementioned instrument for quantitative analysis, the cell and the cell holder can not be accurately arranged at the position in which the sample and/or the reagent are injected into the cell, since the operator can not see into the black box while the cell is moving horizontally into the injecting position. Therefore, the sample and/or the reagent injected into the black box may miss the cell, in which case the cell holder or the inner wall of the black box which are made of metal may be corroded by the sample and/or the reagent. In addition, if the cell is not accurately arranged in the black box, the needle of the pipetting device can not accurately positioned at the injecting position in which the sample and/or the reagent are injected into the cell, so that the sample can not be accurately measured.
Furthermore, when an enzyme is used as a labelling material, the temperature of the reaction system must be constant since the enzyme activity is dependent on the temperature. However, conventional cell holders of instruments for quantitative analysis have no system for maintaining temperature therein. Therefore, the quantity of emitted light measured in the conventional instruments is not a dependable value.